1. Field of the Invention
The present invention relates to a laser device in which an AC discharge between opposing electrodes is used as a laser exciting source, and more specifically, to an improvement in supplying discharge power to the electrodes in a laser device.
2. Description of the Prior Art
In a conventional laser device, an AC voltage outputted from a switching circuit (inverter) for DC/AC conversion is applied to opposing discharge electrodes of a laser oscillator to generate an AC discharge therebetween to use it as a laser exciting source.
However, such a conventional laser device has disadvantages in the following respects because the AC voltage applied from the switching circuit to the discharge electrodes has a square or the similar waveform.
(a) Since a discharge current caused by the AC square-waveform voltage contains harmonic components of large amplitude, the laser device produces a high level high frequency noise (harmonic noise) during discharging operation.
(b) Since the discharge part is a capacitive load, the concentrated discharge current flows during a short rise time of the square-waveform voltage and thus the discharge current has a high peak value, which disadvantageously results in that the discharge electrodes are likely to be damaged and switching elements and diodes for protection of these elements in the switching circuit are quickly deteriorated.
(c) The discharge current having a high peak value strongly tends to cause a discharge transition, thus lowering an oscillation efficiency.
The discharge transition means a transfer of the mode of discharge from glow discharge to other modes such as arc discharge having a very high current density. When such transition takes place, most of the discharge power is consumed for raising the temperature of a laser medium gas, whereby the excitation efficiency is greatly reduced and the oscillation is sometimes disabled.